Conventional organic thin films such as polarizing films have been required to satisfy both of the following requirements: the films should be free of appearance defects such as cracks; the films should have sufficient durability to humidity. For example, a known water-resistant polarizing film is obtained by applying a solution to the surface of a polarizing film including an organic dye having an anionic group, in which the solution contains two organic nitrogen compounds having two or more nitrogen atoms (see, for example, Patent Document 1).
Another known water-resistant polarizing film is obtained applying a solution to the surface of a polarizing film including an organic dye having an anionic group, in which the solution contains an acyclic compound having two to five nitrogen atoms, and a further known polarizing film is obtained by bringing a cationic polymer-containing liquid into contact with the surface of a polarizing film including an organic dye having an anionic group (see, for example, Patent Documents 2 and 3).
Unfortunately, the polarizing films disclosed in Patent Documents 1 to 3 have problems in that they can be not only cracked, but also eroded at their end part by water in a humidity test so that the molecules at the end part can be out of alignment to become almost optically isotropic. In addition, as water-induced erosion proceeds, the end parts of the films are dissolved and partially chipped in some cases.